What was done
Bell pepper (Capsicum annuum L. cv. Mazurka) plants were grown under optimal environmental conditions until eight days prior to anthesis, at which time they were placed in greenhouses receiving atmospheric CO2 concentrations of either 350 or 800 ppm and normal (28/22°C) or elevated (32/26°C) day/night air temperatures to determine the effects of these two parameters on various reproductive parameters associated with pollen, which is very sensitive to high temperature.

What was learned
Although many observations were made in this study, only two were of great importance.  First, high temperature stress reduced pollen germination by 75% at ambient CO2; but atmospheric CO2 enrichment completely ameliorated this negative effect.  Second, high temperature reduced the number of seeds produced per fruit by 68%, while elevated CO2 nearly ameliorated this effect, reducing the temperature-induced seed-per-fruit reduction to only 9%.

What it means
As the CO2 content of the air continues to rise, the reproductive fitness of bell pepper plants (and possibly other plants) should not be harmed by any global warming that might occur, regardless of its cause; while in warmer regions of a non-warming world, elevated CO2 concentrations could actually enhance reproductive fitness, making it possible for certain plants to grow and reproduce where it has previously been too warm for them to do so.